ECE 4400:427/527 - Computer Networks Spring 2017 Dr. Nghi Tran Department of Electrical & Computer Engineering Lecture 3: Network Architectures Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Some Discussions We know that there are substantial requirements for NETWORK DESIGN General, cost-effective, fair, robust connectivity among large computers/users Should be manageable by humans of varying levels of skills Network designers have developed general blueprints referred to as NETWORK ARCHITECTURES to deal with complexity Guide the design and implementation of networks Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Outline In this lecture, we introduce some central ideas common to all network architecture Layering Protocols We also consider two most widely referenced architectures: The OSI -7 –layer Internet architecture Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Layering Communication network is so complex Contain many pieces: hosts, switching devices, channels, etc How we can manage complexity? Using divide and conquer approach: Idea of Layering Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Example of Air Travel Travelling contain a series of steps Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

intermediate air-traffic Layering of Air Travel ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival intermediate air-traffic control centers ticket (complain) baggage (claim gates (unload) runway (land) ticket baggage gate takeoff/landing Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Why Layering? Dealing with complex systems: Explicit structure allows identification, relationship of complex system’s pieces Layered reference model for discussion Modularization eases maintenance, updating of system change of implementation of layer’s service transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system Layering considered harmful? Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Layering Abstraction Layer: A set of functionalities encapsulated in an object that can be used by other network components Why layering? Think complexity and common services Layers consist of protocols Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Protocols Protocol defines the interfaces between the layers in the same system and with the layers of peer system Building blocks of a network architecture Each protocol object has two different interfaces service interface: operations on this protocol peer-to-peer interface: messages exchanged with peer Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Protocols Protocols in each layer have Service interface with upper layer/lower layers Peer-to-peer interface with host on same layer Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Hierarchical Layer Structure Layering implies the use of a layer hierarchy Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

OSI – Open Systems Interconnection OSI 7-Layer Model First formal way defined to connect computers One or more protocols implement the functionality assigned to a given layer Acts like a reference model rather than a real-world protocol graph First three layers are implemented in all network nodes The OSI 7-layer Model OSI – Open Systems Interconnection Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Description of Layer Physical Layer Data Link Layer Network Layer Handles the transmission of raw bits over a communication link Data Link Layer Collects a stream of bits into a larger aggregate called a frame Network adaptor along with device driver in OS implement the protocol in this layer Frames are actually delivered to hosts Network Layer Handles routing among nodes within a packet-switched network Unit of data exchanged between nodes in this layer is called a packet The lower three layers are implemented on all network nodes Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Description of Layer Transport Layer Session Layer Presentation Layer Implements a process-to-process channel Unit of data exchanges in this layer is called a message Session Layer Provides a name space that is used to tie together the potentially different transport streams that are part of a single application, e.g., synchronization Presentation Layer Concerned about the format of data exchanged between peers, e.g., encryption, compression Application Layer Standardize common type of exchanges The transport layer and the higher layers typically run only on end-hosts and not on the intermediate switches and routers Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

The Internet Architecture Application: supporting network applications FTP, SMTP, HTTP Transport: process data transfer TCP, UDP Network: routing of datagrams from source to destination IP, routing protocols Link: data transfer between neighboring network elements Ethernet, 802.111 (WiFi), PPP Physical: bits “on the wire” Application Transport Network Link Physical Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Internet Architecture vs OSI Presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions Session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! These services, if needed, must be implemented in application Application Presentation Session Transport Network Link Physical Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

The Internet: Protocol Encapsulation source message M application transport network link physical segment Ht M Ht datagram Ht Hn M Hn frame Ht Hn Hl M link physical Ht Hn Hl M Ht Hn Hl M switch destination network link physical Ht Hn M Ht Hn M M application transport network link physical Ht Hn Hl M Ht Hn Hl M Ht M Ht Hn M router Ht Hn Hl M Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

Protocol Encapsulation: Example A in Office 1 sends to B in Office 2 a memo Memo: Application-layer message Memo needs to placed on an interoffice envelope and A needs to write an address: Envelope: Transport-layer segment, with header is A’s address Envelope headed to sending office mailroom and placed in a postal envelope; suited for public postal service: Datagram Sending to receiving office mailroom: De-encapsulation begins. B will finally get the memo. Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

The Internet: Alternative View FTP HTTP TFTP DNS TCP UDP IP Net 1 Net 1 Ethernet FDDI FTP: File Transfer Protocol HTTP: Hypertext Transport Protocol TFTP: Trivial File Transfer Protocol FDDI: Fiber Distributed Data Interface TCP: Transmission Control Protocol UDP: User Datagram Protocol IP: Internet Protocol Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

The Internet: Alternative View Subnetwork: Involve sublayers Internet Protocol: Support the interconnection of multiple networking technologies into a single, logical internetwork TCP/UDP: Two main protocols of third layer TCP: provide a reliable byte-stream channel UDP: provide an unreliable datagram delivery channel Sometimes called end-to-end protocols Application We will step by step go through those layers/protocols Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527

TCP vs. UDP TCP: most commonly used protocol on the Internet UDP: Source: Skullbox.net TCP: most commonly used protocol on the Internet UDP: Important data? For streaming audio and video; UDP packets in Denial of Service (DoS); also implemented in trojan horse viruses etc. Again, we will step by step go through all these Dr. Nghi Tran (ECE-University of Akron) ECE 4400:427/527